We now have received about 200 sets of x-rays. Most have been very good, but some have had problems and considering the discomfort or stress for the dogs, the trouble to which you go, and our expense, it seemed wise to share some common problems and their remedies in the probable event that you will be taking x-rays of other dogs for the project. (We currently plan to obtain radiographs of about 600 dogs.)
 

    First let me remind you of the goal: To obtain 2 good x-rays of the head (all parts and a few of the vertebrae in the neck); a good x-ray of the hip complex (pelvis); a good x-ray of the fore limb including the shoulder socket and head of the humerus as well as the toe digits; and a good x-ray of the hind limb including the hip socket, and head of the femur and the toes. All of these parts are important. Also the exposure-resolution should be such that we can see the humerus and femur structures as cylinders from which we can measure the thickness of the actual bone (the edge) in order to calculate the strength of the bone. It is important to follow the same procedure in all radiograms because we will be comparing a large number of PWDs and we would like the differences to be due to their anatomy and not to changes in the procedure. Remember, if a limb or other part of the anatomy is at an angle toward the camera, it will appear distorted in the radiogram. From a good set of radiograms we can obtain as many as 70 different anatomical phenotypic measurements.
 

    Common problems are placement of limbs such that shoulder or hip joints are not included and/or toes are not included. Be careful to fold the leg (as in the letter "Z") so as to include the regions requested, but don't cover up the toes with a lead glove. For the head, a common problem has been the use of smaller plates with the consequence that edges of the skull often have been cut off (frequently the chin). Those who have used a large plate usually do not have this difficulty.
 

    In one or two cases, legs were at an angle off of the radiograph plate causing a distorted view. In many cases (at least half) the lateral view of the head was at an angle to the camera. This may cause minor problems in those measurements. It is usually easy to see this in the picture because the palate appears as a thick bar or even two lines and the two rows of teeth on either side of the head appear separated. A somewhat more serious problem, but fortunately less frequent has been lateral tilting of the head in the ventral dorsal view. This immediately is apparent as a distortion in which bilateral symmetry is lost(especially apparent in the dentition (canines) and one side is narrower than the other). Such a distortion invalidates all width measurements and is serious because it cannot be repeated without anesthetic or tranquilizer.
 

    Finally, under exposure washes out detail at the shoulder or hip joints, while over exposure can darken the image to such a degree that it is impossible to image the radiogram for the computer.
 

    We know that if care is taken these problems are avoidable, because more than half of the x-rays have been excellent.

    Please remember that the sooner we see the pictures, the sooner we can feed back any corrections that may be necessary.
 

Karl G. Lark
Distinguished Professor